|[AMRadio] Antenna tuner info|
gswynar at durham.net
Wed Jan 10 10:55:32 EST 2007
In the matter of rope, do NOT use polypropylene! (that's the commonly yellow
stranded stuff) --- it may be "penny-wise" & cheap at the outset, but it's
"pound-foolish" & costly in the long run...especially when the darn stuff
comes apart right at the height of the low band DX season (like mine did
Polyprop is VERY sensitive to UV deterioration --- I give it a "healthy"
lifespan of no more than two years out-of-doors. For my money, I spend the
50% - 100% extra & go with NYLON rope. It's not exotic, it's readily
available, & just like the Everyready bunny, it just keeps going, and going,
~73~ Eddy VE3CUI - VE3XZ
----- Original Message -----
From: "Geoff/W5OMR" <ars.w5omr at gmail.com>
To: "Discussion of AM Radio in the Amateur Service"
<amradio at mailman.qth.net>
Sent: Wednesday, January 10, 2007 10:08 AM
Subject: Re: [AMRadio] Antenna tuner info
> Brett gazdzinski wrote:
> > As I think about building a tuner, I was
> > wondering what size components would be needed
> > for my power levels.
> Make everything capable of handling your maximum output, x2.
> ie: if the B+ on a capacitor in a modulated stage should be 2500v, use
> one rated for 5kV.
> > The pair of 813's can run up to 700 watts
> > of carrier output, but I usually turn it down
> > to about 500 watts out, around 1500 watts pep.
> You do realize that this is less than 100% of audio, correct?
> 100w of carrier, modulated to 100% = 400w PEP
> > the antenna will likely be about 100 feet
> > in a flat top setup, up about 30 feet, fed with
> > about 30 feet of open wire line, made with #12
> > wire spaced an inch or two apart.
> John/WA5BXO built an antenna for 'portable' use, which is about as you
> are describing. Except, his feedline is a pair of 12ga stranded lines,
> spaced around 4 or 5 inches apart. Being in the Computer Repair and
> service business, he had access to 'boxes' full of drive-bay covers.
> So, whatever that distance is, is about where his feedline is spaced.
> 5.25"? Those drive-bay covers also make it easier to roll up the feed
> line, but experience has proven over time that they are just as subject
> to the rigors of UV light.
> > Cardwell is selling new caps, model 153-11-1 100pf 7000 volt
> > for about $100.00 (for a shiny new cap).
> Man... couldn't you take some older oil-filled caps, and series/parallel
> 'em to get the same value at about $5.oo (or less) per at a Hamfest?
> > Would 7000 volts be enough for most situations?
> > What size copper wire to make the coil with?
> > Bigger is likely better, but what is the minimum
> > size that would work, #12, #10?
> If it's available, Brett, I'd be tempted to use 8ga solid copper wire.
> > Does anyone know what sort of parts were used in the
> > Johnson KW matchbox?
> > The ARRL handbook says for 250 watts of AM, 4500 volt
> > caps and #14 wire are good.
> You know, lots of tuners were made by simply tapping an air-dux coil.
> Whatever the size of most of those, then, should be sufficient.
> > Or, what do you guys use for GOOD wire and rope?
> > The rope is in tree's, and the wind rubs it some,
> > the best stuff from home depot holds up 4 or 5 years
> > before it looks bad enough to change out.
> > Anything better out there?
> How about a pulley, tied to a tree, and the end of the rope pulled
> through the pulley, with a weight on the end of it? Let the tree sway -
> the rope will roll back and forth through the pulley and not become
> frayed by rubbing on the tree.
> As far as antenna wire, any conductor will work. I've had fairly good
> luck with simple 10 or 12ga copper wire. Of course, the price of copper
> has gone sky-high. A 500' roll of 12ga insulated copper wire at the
> hardware store used to cost $25.oo. If you want something a little
> larger in size (for a larger surface area - think 'skin effect') guy
> line is a conductor, but it's hard to work with. You would probably
> have to use cable clamps and some conductive grease would help stave off
> corrosion over the years. Guy wire is galvanized and holds up towers
> for years and years and years.
> Hope that helps, Brett...
> 73, etc
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